Prosthetic ball-and-socket joint

ABSTRACT

A prosthetic joint includes: (a) first member having a balanced centroidal axis, and comprising a rigid material and a concave interior defining a cup surface, the cup surface including: (i) a cantilevered first flange defining a wear-resistant protruding first contact rim, the first flange being asymmetric relative to the balanced centroidal axis; and (ii) a cantilevered second flange defining a wear-resistant protruding second contact rim; (b) a second member comprising a rigid material with a wear-resistant, convex contact surface; (c) where the first and second contact rims bear against the contact surface of the second member, to transfer loads between the first and second members, while allowing pivoting motion therebetween; and (d) wherein the flanges are shaped and sized so as to deform elastically and permit the first and second contact rims to conform in an irregular shape to the contact surface, when the joint is under load.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of application Ser. No.12/826,620, filed Jun. 29, 2010, now U.S. Pat. No. 7,914,580, which is aContinuation-in-Part of application Ser. No. 12/714,288, filed Feb. 26,2010, now U.S. Pat. No. 7,905,919 issued Mar. 15, 2011, which is aContinuation-in-Part of application Ser. No. 11/936,601, filed Nov. 7,2007, currently pending, which claims the benefit of Provisional PatentApplication 60/864,667, filed Nov. 7, 2006.

BACKGROUND OF THE INVENTION

This invention relates generally to medical implants, and moreparticularly to prosthetic joints having conformal geometries and wearresistant properties.

Medical implants, such as knee, hip, and spine orthopedic replacementjoints and other joints and implants have previously consisted primarilyof a hard metal motion element that engages a polymer contact pad. Thishas usually been a high density high wear resistant polymer, for exampleUltra-High Molecular Weight Polyethylene (UHMWPE), or other resilientmaterial. The problem with this type of configuration is the polymereventually begins to degrade due to the caustic nature of blood, thehigh impact load, and high number of load cycles. As the resilientmember degrades, pieces of polymer may be liberated into the joint area,often causing accelerated wear, implant damage, and tissue inflammationand harm.

It is desirable to employ a design using a hard member on a hard member(e.g. metals or ceramics), thus eliminating the polymer. Such a designis expected to have a longer service life. Extended implant life isimportant as it is now often required to revise or replace implants.Implant replacement is undesirable from a cost, inconvenience, patienthealth, and resource consumption standpoint.

Implants using two hard elements of conventional design will be,however, subject to rapid wear. First, a joint having one hard, rigidelement on another will not be perfectly shaped to a nominal geometry.Such imperfections will result in points of high stress, thus causinglocalized wear. Furthermore, two hard elements would lack the resilientnature of a natural joint. Natural cartilage has a definite resilientproperty, absorbing shock and distributing periodic elevated loads. Thisin turn extends the life of a natural joint and reduces stress onneighboring support bone and tissue. If two rigid members are used, thisability to absorb the shock of an active lifestyle could be diminished.The rigid members would transmit the excessive shock to the implant tobone interface. Some cyclical load in these areas stimulates bone growthand strength; however, excessive loads or shock stress or impulseloading the bone-to-implant interface will result in localized bone massloss, inflammation, and reduced support.

BRIEF SUMMARY OF THE INVENTION

These and other shortcomings of the prior art are addressed by thepresent invention, which provides a prosthetic joint havingwear-resistant contacting surfaces with conformal properties.

According to one aspect of the invention, a prosthetic joint includes:(a) first member having a balanced centroidal axis, the first membercomprising a rigid material and including a concave interior defining acup surface, the cup surface including: (i) a cantilevered first flangedefining a wear-resistant first contact rim which protrudes relative anominal profile of the cup surface, the first flange being asymmetricrelative to the balanced centroidal axis; and (ii) a cantilevered secondflange defining a wear-resistant second contact rim which protrudesrelative to the nominal profile of the cup surface; (c) where the firstand second contact rims bear directly against the contact surface of thesecond member, so as to transfer axial and lateral loads between thefirst and second members, while allowing pivoting motion between thefirst and second members; and (d) wherein the flanges are shaped andsized so as to deform elastically and permit the first and secondcontact rims to conform in an irregular shape to the contact surface,when the joint is placed under a predetermined load.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reference to the followingdescription taken in conjunction with the accompanying drawing figuresin which:

FIG. 1 is a cross-sectional view of a portion of a resilient contactmember constructed in accordance with the present invention;

FIG. 2 is an enlarged view of the contact member of FIG. 1 in contactwith a mating joint member;

FIG. 3 is a side view of a resilient contact member in contact with amating joint member;

FIG. 4 is a cross-sectional view of a cup for an implant according to analternate embodiment of the invention;

FIG. 5 is an enlarged view of a portion of the cup of FIG. 4;

FIG. 6 is a perspective view of a finite element model of a jointmember;

FIG. 7 is a cross-sectional view of an implant joint including aflexible seal;

FIG. 8 is an enlarged view of a portion of FIG. 7;

FIG. 9 is a side view of a prosthetic joint constructed in accordancewith an aspect of the present invention;

FIG. 10 is a cross-sectional view of the prosthetic joint of FIG. 9 inan unloaded condition;

FIG. 11 is a cross-sectional view of one of the members of theprosthetic joint of FIG. 9;

FIG. 12 is an enlarged view of a portion of FIG. 10;

FIG. 13 is a cross-sectional view of the prosthetic joint of FIG. 9 in aloaded condition;

FIG. 14 is an enlarged view of a portion of FIG. 13;

FIG. 15 is a cross-sectional view of an alternative joint member;

FIG. 16 is an enlarged view of a portion of FIG. 15;

FIG. 17 is a cross-sectional view of another alternative joint member;

FIG. 18 is a cross-sectional view of another alternative joint memberincluding a filler material;

FIG. 19 is a cross-sectional view of another alternative joint memberincluding a wiper seal;

FIG. 20 is a cross-sectional view of another alternative prostheticjoint;

FIG. 21 is a cross-sectional view of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 22 is a cross-sectional view of a prosthetic joint constructed inaccordance with yet another aspect of the present invention; and

FIG. 23 is a perspective view of a joint member having a groovedsurface.

FIG. 24 is a exploded perspective view of two mating joint members;

FIG. 25 is a top plan view of one of the joint members shown in FIG. 24;

FIG. 26 is a cross-sectional view of one of the joint members shown inFIG. 24;

FIG. 27 is a contact stress plot of the joint member shown in FIG. 26;

FIG. 28 is a perspective view of a rigid joint member used forcomparison purposes;

FIG. 29 is a cross-sectional view of the joint member shown in FIG. 28;and

FIG. 30 is a contact stress plot of the joint member shown in FIG. 29;

FIG. 31 is a cross-sectional view of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 32 is an enlarged view of a portion of the joint shown in FIG. 31;

FIG. 33 is a cross-sectional view of a cup member of the joint shown inFIG. 31;

FIG. 34 is a greatly enlarged cross-sectional view of a portion of thejoint shown in FIG. 31 in an initial condition;

FIG. 35 is a greatly enlarged cross-sectional view of a portion of thejoint shown in FIG. 31 after an initial wear-in period;

FIG. 36 is a graph showing contact pressure of the joint of FIG. 31compared to the number of operating cycles;

FIG. 37 is a cross-sectional view of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 38 is an enlarged view of a portion of the joint shown in FIG. 37

FIG. 39 is a cross-sectional view of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 40 is a cross-sectional view of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 41 is a plan view of a portion of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 42 is a view taken along lines 42-42 of FIG. 41;

FIG. 43 is a view taken along lines 43-43 of FIG. 41;

FIG. 44 is a cross-sectional view of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 45 is a perspective view of the prosthetic joint of FIG. 44;

FIG. 46 is a perspective view of a prosthetic joint constructed inaccordance with another aspect of the present invention;

FIG. 47 is a cross-sectional view of the prosthetic joint of FIG. 46;

FIG. 48 is a sectional perspective view of a prosthetic jointconstructed in accordance with another aspect of the present invention;

FIG. 49 is an enlarged portion of the joint of FIG. 48, showing a rimconfiguration thereof;

FIG. 50 is a sectional perspective view showing an alternative rimconfiguration for use with the joint shown in FIG. 49;

FIG. 51 is a sectional perspective view showing another alternative rimconfiguration for use with the joint shown in FIG. 49;

FIG. 52 is a sectional perspective view of a member of a prostheticjoint with an aperture formed therein;

FIG. 53 is a cross-sectional view of a prosthetic joint showing amulti-piece construction;

FIG. 54 is a cross-sectional view of a prosthetic joint constructed inaccordance with another aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a specialized implant contact interface(implant geometry). In this geometry, an implanted joint includes twotypically hard (i.e. metal or ceramic) members; however, at least one ofthe members is formed such that it has the characteristics of aresilient member, such as: the ability to absorb an impact load; theability to absorb high cycle loading; the ability to be self-cleaning;and the ability to function as a hydrodynamic and/or hydrostaticbearing.

Generally, the contact resilient member is flexible enough to allowelastic deformation and avoid localized load increases, but not soflexible as to risk plastic deformation, cracking and failure. Inparticular, the resilient member is designed such that the stress levelstherein will be below the high-cycle fatigue endurance limit. As anexample, the resilient member might be only about 10% to about 20% asstiff as a comparable solid member. It is also possible to construct theresilient member geometry with a variable stiffness, i.e. having a loweffective spring rate for small deflections and a higher rate as thedeflections increase, to avoid failure under sudden heavy loads.

FIG. 1 illustrates an exemplary contact member 34 including a basicresilient interface geometry. The contact member 34 is representative ofa portion of a medical implant and is made of one or more metals orceramics (for example, partially stabilized Zirconia). It may be coatedas described below. The geometry includes a lead-in shape, Z1 and Z2, acontact shape, Z3 and Z4, a lead-out shape, Z5 and Z6, and a relievedshape, Z7. It may be desired to vary the cross-sectional thickness toachieve a desired mechanical stiffness to substrate resiliencecharacteristic. The presence of the relieved region Z7 introducesflexibility into the contact member 34, reduces the potential forconcentrated point contact with a mating curved member, and provides areservoir for a working fluid.

The Z7 region may be local to the contact member 34 or may be one ofseveral. In any case, it may contain a means of providing fluid pressureto the internal contact cavity to produce a hydrostatic interface. Apassive (powered by the regular motion of the patient) or active(powered by micro components and a dedicated subsystem) pumping meansand optional filtration may be employed to provide the desired fluidinteraction.

A hydrodynamic interface is desirable as, by definition, it means thecontact member 34 is not actually touching the mating joint member. Thelead-in and lead-out shapes Z1, Z2, Z5, Z6 are configured to generate ashear stress in the working fluid so as to create the fluid “wedge” of ahydrodynamic support.

FIG. 2 shows a closer view of the contact member 34. It may be desirableto make the contact radius (Z3 and Z4) larger or smaller, depending onthe application requirement and flexural requirement. For example, FIG.3 illustrates the contact member 34 in contact with a mating jointmember 38 having a substantially larger radius than the contact member34. The radius ratio between the two joint members is not particularlycritical, so long as one of the members exhibits the resilientproperties described herein.

The contact member 34 includes an osseointegration surface “S”, which isa surface designed to be infiltrated by bone growth to improve theconnection between the implant and the bone. Osseointegration surfacesmay be made from materials such as TRABECULAR METAL, textured metal, orsintered or extruded implant integration textures. TRABECULAR METAL isan open metal structure with a high porosity (e.g. about 80%) and isavailable from Zimmer, Inc., Warsaw, Ind. 46580 USA.

FIGS. 4 and 5 illustrate a cup 48 of metal or ceramic with twointegrally-formed contact rings 50. More contact rings may be added ifneeded. As shown in FIG. 5, the volume behind the contact rings 50 maybe relieved. This relieved area 52 may be shaped so as to produce adesired balance between resilience and stiffness. A varyingcross-section geometry defined by varying inner and outer spline shapesmay be desired. In other words, a constant thickness is not required. Amaterial such as a gel or non-Newtonian fluid (not shown) may bedisposed in the relieved area 52 to modify the stiffness and dampingcharacteristics of the contact rings 50 as needed for a particularapplication. The cup 48 could be used as a stand-alone portion of ajoint, or it could be positioned as a liner within a conventional liner.The contact ring 50 is shown under load in FIG. 6, which depicts contourlines of highest compressive stress at “C1”. This is the portion of thecontact ring 50 that would be expected to undergo bending first. Thebearing interface portion of the resilient contact member could beconstructed as a bridge cross-section supported on both sides as shownor as a cantilevered cross-section depending on the desired static anddynamic characteristics.

FIGS. 7 and 8 illustrate an implant 56 of rigid material which includesa wiper seal 58. The wiper seal 58 keeps particles out of the contactarea (seal void) 60 of the implant 58, and working fluid (natural orsynthetic) in. The seal geometry is intended to be representative and avariety of seal characteristics may be employed; such as a single lipseal, a double or multiple lip seal, a pad or wiper seal made from avariety of material options. Different seal mounting options may beused, for example a lobe in a shaped groove as shown in FIGS. 7 and 8, aretaining ring or clamp, or an adhesive. The wiper seal 58 may also beintegrated into the contact face of the interface zone.

It may be desirable to create a return passage 62 from the seal voidregion 60 back into the internal zone 64 in order to stabilize thepressure between the two and to allow for retention of the internal zonefluid if desired. This is especially relevant when the hydrostaticconfiguration is considered.

FIGS. 9-14 illustrate a prosthetic joint 100 comprising first and secondmembers 102 and 104. The illustrated prosthetic joint 100 isparticularly adapted for a spinal application, but it will be understoodthat the principles described herein may be applied to any type ofprosthetic joint. Both of the members 102 and 104 may bebone-implantable, meaning they include osseointegration surfaces,labeled “S”, which are surfaces designed to be infiltrated by bonegrowth to improve the connection between the implant and the bone.Osseointegration surfaces may be made from materials such as TRABECULARMETAL, textured metal, or sintered or extruded implant integrationtextures, as described above. As shown in FIG. 10, a central axis “A”passes through the centers of the first and second members 102 and 104and is generally representative of the direction in which external loadsare applied to the joint 100 in use. In the illustrated examples, thefirst and second joint members are bodies of revolution about this axis,but the principles of the present invention also extend to shapes thatare not bodies of revolution.

The first member 102 includes a body 106 with a perimeter flange 116extending in a generally radially outward direction at one end.Optionally, a disk-like base 108 may be disposed at the end of the body106 opposite the flange 116, in which case a circumferential gap 111will be defined between the base 106 and the flange 116. The firstmember 102 is constructed from a rigid material. As used here, the term“rigid” refers to a material which has a high stiffness or modulus ofelasticity. Nonlimiting examples of rigid materials having appropriatestiffness for the purpose of the present invention include stainlesssteels, cobalt-chrome alloys, titanium, aluminum, and ceramics. By wayof further example, materials such as polymers would generally not beconsidered “rigid” for the purposes of the present invention. Generally,a rigid material should have a modulus of elasticity of about 0.5×10⁶psi or greater. Collectively, one end of the body 106 and the flange 116define a wear-resistant, concave first contact surface 118. As usedherein, the term “wear-resistant” refers to a material which isresistant to surface material loss when placed under load. Generally thewear rate should be no more than about 0.5 μm (0.000020 in.) to about1.0 μm (0.000040 in.) per million cycles when tested in accordance withASTM Guide F2423. As a point of reference, it is noted that any of thenatural joints in a human body can easily experience one millionoperating cycles per year. Nonlimiting examples of wear-resistantmaterials include solid metals and ceramics. Known coatings such astitanium nitride, chrome plating, carbon thin films, and/or diamond-likecarbon coatings may be used as a face layer to impart wear resistance tothe first contact surface 118. Optionally, the first contact surface 118could comprise a substantially thicker face layer (not shown) of awear-resistant material such as ultra-high molecular weight (UHMW)polyethylene.

The first contact surface 118 includes a protruding peripheral rim 120(see FIG. 11), and a recessed central portion 122, which may also beconsidered a “pocket” or a “relief”. As used herein, the term “recessed”as applied to the central portion 122 means that the central portion 122lies outside of the nominal exterior surface of the second member 104when the joint 100 is assembled. The terms “recessed” and “protruding”as used herein are opposite in meaning to one another. For example, theperipheral rim 120 protrudes relative to a nominal surface defined bythe central portion 122, and the central portion 122 is recessedrelative to the rim 120. In one configuration, shown in FIGS. 9-14, andbest seen in FIG. 11, the rim 120 is concave, with the radius ofcurvature being quite high, such that the cross-sectional shape of thesurface of the rim 120 approaches a straight line. FIGS. 15 and 16 showanother configuration of a joint member 102′ with a flange 116′ in whichthe rim 120′ has a convex-curved cross-sectional shape. Thecross-sectional shape of the rim may be flat or curved as necessary tosuit a particular application.

The annular configuration of first contact surface 118 with theprotruding rim 120 results in a configuration which permits onlypivoting and rotational motion, and is statically and dynamicallydeterminate for the life of the joint 100. In contrast, prior artdesigns employing mating spherical shapes, even very accurate shapes,quickly reach a statically and dynamically indeterminate condition afteruse and wear. This condition accelerates wear, contributes to thefretting corrosion wear mechanism, and permits undesired lateraltranslation between the joint members.

The second member 104 is also made from a rigid material and has awear-resistant, convex second contact surface 124. The first and secondcontact surfaces 118 and 124 bear directly against each other so as totransfer axial and lateral loads from one member to the other whileallowing pivoting motion between the two members 102 and 104.

Nominally the first and second members 102 and 104 define a “ring” or“band” contact interface therebetween. In practice it is impossible toachieve surface profiles completely free of minor imperfections andvariations. If the first and second members 102 and 104 were bothcompletely rigid, this would cause high Hertzian contact stresses andrapid wear. Accordingly, an important feature of the illustrated joint100 is that the flange 116 (and thus the first contact surface 118) ofthe first member 102 is conformable to the second contact surface 124when the joint is placed under load.

FIGS. 10 and 12 show a cross-sectional view of the flange 116 in anunloaded condition or free shape. It can be seen that the distal end ofthe rim 120 contacts the second contact surface 124, while the inboardend of the rim 120 (i.e. near where the flange 116 joins the body 106)does not. FIGS. 13 and 14 show the flange 116 in a deflected position orloaded shape, where substantially the entire section width of the rim120 contacts the second contact surface 124, resulting in asubstantially increased contact surface area between the two members 102and 104, relative to the free shape. The rim 120′ of the joint member102′ (see FIG. 16) is similarly conformable; however, given the curvedcross-sectional shape, the total amount of surface contact area remainssubstantially constant in both loaded and unloaded conditions, with therim 120′ undergoing a “rolling” or “rocking” motion as the loadingchanges.

The conformable nature of the flange 116 is explained in more detailwith reference to FIGS. 24 through 30. As noted above, the first member102 has a flange 116 and a concave first contact surface 118. The secondmember 104 has a convex second contact surface 124. When assembled andin use the joint 100 is subject, among other loads, to axial loading inthe direction of the arrows labeled “F” in FIG. 24 (i.e. along axis “A”of FIG. 10). As previously stated, it is impossible in practice foreither of the contact surfaces 118 or 124 to be perfect surfaces (i.e. aperfect sphere or other curve or collection of curves). It is believedthat in most cases that a defect such as a protrusion from the nominalcontact surface of just 0.00127 mm (0.00005 in.), that is, 50 millionthsof an inch, or larger, would be sufficient to cause fretting corrosionand failure of a metal-on-metal joint constructed to prior artstandards. A defect may include a variance from a nominal surface shapeas well as a discontinuity in the contact surface. Defects may arisethrough a variety of sources such as manufacturing, installation, and/oroperating loads in the implanted joint.

FIG. 25 shows the second member 104 which in this particular examplevaries from a nominal shape in that it is elliptical rather thancircular in plan view. The elliptical shape is grossly exaggerated forillustrative purposes. For reference, the dimensions of the secondmember 104 along the major axis labeled “X” is about 0.0064 mm (0.00025in.) larger than its dimension along the minor axis labeled “Y”. Whenassembled and loaded, the flange 116 conforms to the imperfect secondcontact surface 124 and deflects in an irregular shape. In other words,in addition to any uniform deflection which may be present, thedeflected shape of the flange 116 includes one or more specificlocations or portions that are deflected towards or away from thenominal free shape to a greater or lesser degree than the remainder ofthe flange 116. Most typically the deflected shape would be expected tobe non-axisymmetric. For example, the deflection of the flange 116 atpoints located at approximately the three o'clock and nine o'clockpositions is substantially greater than the deflection of the remainderof the flange 116. As a result, the contact stress in that portion ofthe first contact surface 118 is relieved. FIG. 27 is a plan view plot(the orientation of which is shown by arrow in FIG. 26) whichgraphically illustrates the expected contact stresses in the firstcontact surface 118 as determined by analytical methods. The firstcontour line “C2” shows that a very low level of contract stress ispresent around the entire perimeter of the first contact surface 118.This is because the entire first contact surface 118 is in contact withthe second contact surface 124. Another contour line “C3” represents theareas of maximum contact stress corresponding to the protruding portionsof the elliptical second contact surface 124.

For comparative purposes, FIGS. 28 and 29 depict a member 902constructed according to prior art principles. The member 902 has acontact surface 918 with an identical profile and dimensions of thefirst contact surface 118 of the first member 102. However, consistentwith the prior art, the member 902 has a massive body 920 behind theentire contact surface 918, rendering the entire member 902substantially rigid. FIG. 30 graphically illustrates the expectedcontact stresses in the contact surface 918 as determined by analyticalmethods, when the member 902 is assembled and placed in contact with thesecond member 104, using the same applied load as depicted in FIG. 27.Because of the rigidity of the member 902, a “bridging” effect ispresent wherein contact between the contact surfaces (one of which iscircular in plan view, and the other of which is elliptical) effectivelyoccurs at only two points, located at approximately the three o'clockand nine o'clock positions. A first contour line “C4” shows two discreteareas where the lowest level of contract stress is present. These linesare not contiguous because there is no contact in the remaining area ofthe contact surfaces (for example at the six o'clock and twelve o'clockpositions). Another contour line “C5” represents the areas of maximumcontact stress. Analysis shows a peak contact stress having a magnitudeof two to twenty times (or more) the peak contact stress of theinventive joint as shown in FIG. 27.

To achieve this controlled deflection, the flange 116 is thin enough topermit bending under working loads, but not so thin as to allow materialyield or fatigue cracking. The deflection is opposed by the elasticityof the flange 116 in bending, as well as the hoop stresses in the flange116. To achieve long life, the first member 102 is sized so thatstresses in the flange 116 will be less than the endurance limit of thematerial, when a selected external load is applied. In this particularexample, the joint 100 is intended for use between two spinal vertebrae,and the design average axial working load is in the range of about 0 N(0 lbs.) to about 1300 N (300 lbs.). These design working loads arederived from FDA-referenced ASTM and ISO standards for spinal discprostheses. In this example, the thickness of the flange 116, at a root126 where it joins the body 106 (see FIG. 12) is about 0.4 mm (0.015in.) to about 5.1 mm (0.200 in.), where the outside diameter of theflange 116 is about 6.4 mm (0.25 in.) to about 7.6 cm (3.0 in.).

The joint members may include multiple rims. For example, FIG. 17illustrates a joint member 202 where the first contact surface 218includes two protruding rims 220, with a circumferential groove orrelief area 228 therebetween. The presence of multiple rims increasesthe contact surface areas between the two joint members.

If present, the circumferential gap between the flange and the base ofthe joint member may be filled with resilient nonmetallic material toprovide damping and/or additional spring restoring force to the flange.FIG. 18 illustrates a joint member 302 with a filler 304 of this type.Examples of suitable resilient materials include polymers, natural orsynthetic rubbers, and the like.

As discussed above, the joint may incorporate a wiper seal. For example,FIG. 19 illustrates a joint member 402 with a resilient wiper seal 404protruding from the rim 420 of the first contact surface 418. The wiperseal 404 keeps particles out of the contact area (seal void), whilecontaining working fluid (natural or synthetic). The seal geometry isintended to be representative and a variety of seal characteristics maybe employed; such as a single lip seal, a double or multiple lip seal. Apad or wiper seal may be made from a variety of material options.Different seal mounting options may be used, for example a lobe inshaped groove as shown in FIG. 18, a retaining ring or clamp, adhesionsubstance. The seal may also be incorporated into the contact face ofthe interface zone.

The joint construction described above can be extended into a three-partconfiguration. For example, FIG. 20 illustrates a prosthetic joint 500having first, second, and third members 502, 504, and 506. The first andsecond members 502 and 504 are similar in construction to the firstmember 102 described above, and each includes a body 508, an optionaldisk-like base 510, and a flange 512. The flanges 512 definewear-resistant concave first and second contact surfaces 514 and 516,each of which includes a protruding peripheral rim, and a recessedcentral portion as described above. The third member 506 has adouble-convex shape defining opposed wear-resistant, convex third andfourth contact surfaces 524 and 526. The first and second 514 and 516bear against the third and fourth contact surfaces 524 and 526,respectively, so as to transfer axial (i.e. compression) and lateralloads between the first and second members 502 and 504 through the thirdmember 506, while allowing pivoting motion between the members 502, 504,and 506. The first and second contact surfaces 514 and 516 are conformalto the third and fourth contact surfaces 524 and 526 as described inmore detail above.

FIG. 21 illustrates an alternative prosthetic joint 600 comprising firstand second members 602 and 604 constructed from rigid materials. Both ofthe members 602 and 604 may be bone-implantable, meaning they includeosseointegration surfaces, labeled “S”, as described in more detailabove.

The first member 602 is hollow and includes a disk-like base 606 and acup 608, interconnected by a peripheral wall 610. An interior cavity 612is defined between the base 606 and the cup 608. The cup 608 isconstructed from a rigid material and defines a wear-resistant, concavefirst contact surface 614. The first contact surface 614 includes aprotruding peripheral rim 616, and a recessed central portion 618, whichmay also be considered a “pocket” or a “relief”. The rim 616 may have aconical or curved cross-sectional shape. The interior cavity 612 may befilled with resilient nonmetallic material to provide damping and/oradditional spring restoring force to the flange. Examples of suitableresilient materials include polymers, natural or synthetic rubbers, andthe like.

The second member 604 is constructed from a rigid material and has awear-resistant, convex second contact surface 620. The first and secondcontact surfaces 614 and 616 bear directly against each other so as totransfer axial and lateral loads from one member to the other whileallowing pivoting motion between the two members 602 and 604.

As described above with reference to the prosthetic joint 100, the cup606 of the first member 602 is thin enough to permit bending underworking loads, but not so thin as to allow material yield or fatiguecracking. The first contact surface 614 is thus conformable to thesecond contact surface 620 when the prosthetic joint 600 is placed underexternal load.

An inverted configuration of hollow members is also possible. Forexample, FIG. 22 illustrates a prosthetic joint 700 comprising first andsecond members 702 and 704, both constructed of rigid materials. Thefirst member 702 is solid and includes a wear-resistant, concave firstcontact surface 708. The first contact surface 708 includes a protrudingperipheral rim 710, and a recessed central portion 712, which may alsobe considered a “pocket” or a “relief”.

The second member 704 is hollow and includes a dome 714 connected to aperipheral wall 716. An interior cavity 718 is defined behind the dome714. The dome 714 defines a wear-resistant, convex second contactsurface 720, which is shaped and sized enough to permit bending underworking loads, but not so as to allow material yield or fatiguecracking. The second contact surface 720 is thus conformable to thefirst contact surface 708 when the prosthetic joint 700 is placed underexternal load.

The first and second contact surfaces 708 and 720 bear directly againsteach other so as to transfer axial and lateral loads from one member tothe other while allowing pivoting motion between the two members 702 and704.

Any of the contact surfaces described above may be provided with one ormore grooves formed therein to facilitate flow of fluid or debris. Forexample, FIG. 23 illustrates a joint member 800 including a concavecontact surface 802. The contact surface 802 includes a circular groove804, and plurality of generally radially-extending grooves 806 whichterminate at the center of the contact surface 802 and intersect thecircular groove 804.

FIGS. 31-33 illustrate an alternative prosthetic joint 1000 comprisingfirst and second members 1002 and 1004. The illustrated prosthetic joint1000 is particularly adapted for a ball-and-socket joint applicationsuch as is found in a human hip joint (i.e. the acetabulofemoral joint)or shoulder joint (i.e. the glenohumeral joint), but it will beunderstood that the principles described herein may be applied to anytype of prosthetic joint. Both of the members 1002 and 1004 may bebone-implantable, meaning they include osseointegration surfaces,labeled “S”, which are surfaces designed to be infiltrated by bonegrowth to improve the connection between the implant and the bone.Osseointegration surfaces may be made from materials such as TRABECULARMETAL, textured metal, or sintered or extruded implant integrationtextures, as described above. As shown in FIG. 31, a nominal centralaxis “A” passes through the centers of the first and second members 1002and 1004 In the illustrated examples, the first and second joint members1002 and 1004 are bodies of revolution about this axis, but theprinciples of the present invention also extend to non-axisymmetricshapes.

The first member 1002 is constructed from a rigid material as describedabove. The first member 1002 is concave and may generally be thought ofas a “cup”, although it need not have any particular degree ofcurvature. Its interior defines a cup surface 1006 with a nominalprofile shown by the dashed line in FIG. 33. The interior includes anannular first flange 1008 which is located relatively near an apex 1010of the first member 1002 and which extends in a generally radialdirection relative to the axis A. The first flange 1008 is defined inpart by an undercut groove 1012 formed in the first member 1002. Aramped surface 1014 forms a transition from the groove 1012 to thenominal cup surface 1006. The first flange 1008 includes a protrudingfirst contact rim 1016. As used herein, the term “protruding” as appliedto the first contact rim 1016 means that the first contact rim 1016 liesinside of the nominal profile of the cup surface 1006 when the joint1000 is assembled. The first contact rim 1016 may have a curved ortoroidal cross-sectional shape.

The interior also includes an annular second flange 1018 which islocated at or near an outer peripheral edge 1020 of the first member1002 and which extends in a generally axial direction relative to theaxis A. The second flange 1018 is defined in part by an undercut groove1022 formed in the first member 1002. The second flange 1018 includes aprotruding second contact rim 1024. As used herein, the term“protruding” as applied to the second contact rim 1024 means that thesecond contact rim 1024 lies inside of the nominal cup surface 1006 whenthe joint 1000 is assembled. The second contact rim 1024 may have acurved or toroidal cross-sectional shape. Depending on the particularapplication, joint 1000 may include more than two flanges defining morethan two contact rims.

In the illustrated example, the first member 1002 includes a face layer1026 of a known coating such as titanium nitride, chrome plating, carbonthin films, and/or diamond-like carbon coatings, and/or a anothersubstantially thicker wear-resistant material such as ultra-highmolecular weight (UHMW) polyethylene. This face layer 1026 is used toimpart wear resistance, as described above. The face layer 1026 may beextraordinarily thin. In this particular example, its as-appliedthickness is about 0.0041 mm (0.00016 in.), or 160 millionths of an inchthick. The face layer 1026 is applied at a substantially uniformthickness over the surface profile which is defined by machined orformed features of the substrate. Alternatively, and especially if amuch thicker face layer were used, the face layer could be profiled soas to define both the nominal cup surface 1006 and the first and secondcontact rims 1016 and 1024.

The second member 1004 is also made from a rigid material and has awear-resistant, convex contact surface 1028. In the specific exampleillustrated, the second member 1004 includes a face layer 1030 of aknown coating such as titanium nitride, chrome plating, carbon thinfilms, and/or diamond-like carbon coatings, and/or a anothersubstantially thicker wear-resistant material such as ultra-highmolecular weight (UHMW) polyethylene. This face layer 1030 is used toimpart wear resistance, and may be quite thin, as described above. Thefirst and second contact rims 1016 and 1024 bear directly against thecontact surface 1028 so as to transfer axial and lateral loads from onemember to the other while allowing pivoting motion between the twomembers 1002 and 1004.

The annular configuration of contact rims 1016 and 1024 results in ajoint configuration which permits only pivoting and rotational motion,and is statically and dynamically determinate for the life of the joint1000. In particular, the presence of the relatively widely-spacedcontact rims 1016 and 1024, and the peripheral positioning of the secondcontact rim 1024 is highly effective in resisting any translation of thefirst and second members 1002 and 1004 lateral to the axis A.

Nominally the first and second contact rims 1016 and 1024 define twoseparate “ring” or “band” contact interfaces with the contact surface1028 of the second member 1004. In practice it is impossible to achievesurface profiles completely free of minor imperfections and variations.If the first and second members 1002 and 1004 were both completelyrigid, this would cause high Hertzian contact stresses (i.e. non-uniformcontact) and rapid wear. Accordingly, an important feature of theillustrated joint 1000 is that the flanges 1008 and 1018 (and thus thecontact rims 1016 and 1024) of the first member 1002 are conformable tothe contact surface 1028 when the joint 1000 is placed under load. Theflanges 1008 and 1018 can conform to the imperfect contact surface 1028and deflect in an irregular shape. In other words, in addition to anyuniform deflection which may be present, the deflected shape of theflanges 1008 and 1018 can include one or more specific locations orportions that are deflected towards or away from the nominal free shapeto a greater or lesser degree than the remainder of the flanges 1008 and1018. To achieve this controlled deflection, the flanges 1008 and 1018are thin enough to permit bending under working loads, but not so thinas to allow material yield or fatigue cracking, or to exceed theendurance limit of the material. The deflection is opposed by theelasticity of the flanges 1008 and 1018 in bending, as well as the hoopstresses in the flanges 1008 and 1018.

The contact rims 1016 and 1024 are designed in conjunction with thecontact surface 1028 to create a wear characteristic that is constantlydiminishing (similar to an asymptotic characteristic). With reference toFIG. 32, the as-manufactured or initial curvatures (e.g. radii) of thefirst and second contact rims 1016 and 1024, denoted “R” are differentfrom the curvature (e.g. radius) of the contact surface 1028, denoted“r”. It is noted that the direction of curvature (i.e. the convexity orsecond derivative shape) of the first and second contact rims 1016 and1024 may be the same as, or opposite to, that of the contact surface1028 upon initial manufacture. In this example they are opposite. Whenassembled and placed under load, the annular interface between each ofthe contact rims 1016 and 1024 and the contact surface 1028 will have acharacteristic width denoted “W”, (effectively creating a contact band).The initial dimensions R and r are selected such that, even using highlywear-resistant surfaces or coatings, some wear takes place during aninitial wear-in period of movement cycles. As a result, the contact bandwidth W increases during the initial wear-in period. This increasescontact area and therefore decreases contact stress for a given load.After the initial wear-in period (which preferably occurs before thejoint is implanted), the contact band reaches a post wear-in width atwhich the contact stress is below a selected limit, below which the rateof wear in the contacting surfaces approaches a very low number or zero,consistent with a long life of the joint 1000. FIG. 36 illustrates thiswear characteristic, with the limit “L” depicted as a horizontal line.

FIGS. 34 and 35 are schematic views showing the initial wear-in of thesurface of the contact rim 1016 at a microscopic (or nearly microscopic)level. It will be understood that these figures are greatly exaggeratedfor the purposes of illustration. On initial manufacture, as shown inFIG. 34, the curvatures R and r of the contact rim 1016 and the contactsurface 1028 have opposite directions. When assembled, the contact bandwidth W is some nominal value, for example about 0.03 mm (0.001 in.),and the total thickness “T” of the face layer 1026 is at its as-appliedvalue of about 0.0041 mm (0.00016 in.) for example. The action of thewear-in period described causes the face layer 1026 to wear to a shapecomplementary to the contact surface 1028. After this wear-in period thecurvature of the portion of the contact rim 1016 within the contactband, denoted “R′”, and the curvature r of the contact surface 1028 arein the same direction, and the values of the two curvatures aresubstantially the same. For example, the thickness T at the location ofthe contact band may decrease by about 0.0004 mm (0.000014 in.), with acorresponding increase in the width of the contact band W to about 0.2mm (0.008 in.). Analysis shows that this increase in contact band widthand surface area can reduce mean contact pressure by over 80%.

The configuration of the flanges 1008 and 1018 are important indeveloping the constantly diminishing wear characteristics describedabove. In particular, the flanges 1008 and 1018 are sized and shaped sothat deflections of the contact rims 1016 and 1024 under varying loadare always essentially normal to their respective tangent points on theopposing contact surface 1028, as the joint 1000 is loaded and unloaded.This ensures that the position of each of the contact bands remainsconstant and that the contact bands remain substantially uniform aroundthe entire periphery of the joint 1000.

An inverted configuration of the joint described above may be used. Forexample, FIGS. 37 and 38 illustrate a prosthetic joint 1100 having firstand second members 1102 and 1104 which are substantially similar ingeneral construction to the members of the joint 1000 described above interms of materials, coatings, and so for forth. However, in this joint1100, the concave member 1102 has a contact surface without protrudingrings. The convex member 1104 has first and second flanges 1108 and 1118which define first and second contact rims 1116 and 1124 which functionin the same manner that the flanges and contact rims described above.

FIG. 39 illustrates an alternative prosthetic joint 1200 comprisingfirst and second members 1202 and 1204. The illustrated prosthetic joint1200 is generally similar in construction and function to the prostheticjoint 1000 described above, and one or both of the members 1202 and 1204may be bone-implantable as described above.

For purposes of explanation and illustration the first member 1202 willbe described relative to a “balanced centroidal axis”, labeled “N1” inFIG. 39, passing through it. As used herein, the term “balancedcentroidal axis” refers to a virtual line, parallel to local gravity(i.e. a local vertical), which passes through the geometric centroid ofthe first member 1202, labeled “C”, when the first member is in abalanced position (i.e. when there is no rotation of the first memberdue to unbalanced mass). It is noted that, where the first member 1202is presumed to have a uniform density, the centroid C will be co-locatedwith its center of mass. If the first member 1202 were suspended in abalanced condition by a point “P” vertically above the centroid C, thebalanced centroidal axis N1 would coincide with a local vertical axispassing through the centroid C. In the case where the first member 1202is a body of revolution, the balanced centroidal axis N1 would coincideor nearly coincide with the generating axis of the first member 1202.

The first member 1202 is constructed from a rigid material and maygenerally be thought of as a “cup”, as described above. Its interiordefines a wear-resistant cup surface 1206 including a nominal profile.The interior includes a cantilevered first flange 1208, defined in partby an undercut groove 1212 formed in the first member 1202. Withoutregard to the exact direction that the flange 1208 extends, it may beconsidered to be cantilevered relative to the remainder of the firstmember 1202. In other words, when viewed in cross-section, it is aprojecting structure, that is supported at one end and carries a load atthe other end or along its length. A ramped surface 1214 forms atransition from the groove 1212 to the cup surface 1206. The firstflange 1208 includes a protruding first contact rim 1216. “protruding”has the meaning described above, i.e. the contact rim 1216 extends awayfrom the nominal profile of the cup surface 1206 and towards the secondmember 1204. The first contact rim 1216 may have a straight, curved, ortoroidal cross-sectional shape.

The first flange 1208 has an angular offset relative to the balancedcentroidal axis N1. In other words, the first flange 1208 is asymmetricto the balanced centroidal axis N1. This is also referred to as a“non-axisymmetric” condition. In the particular example and view shownin FIG. 39, the first flange 1208 is offset to the right side of thefigure. The angular offset or asymmetric position allows the functionalcharacteristics of the first flange 1208 to be tailored to specificoperating conditions encountered by the prosthetic joint 1200. Forexample, the angular offset may be selected so that the first flange isaligned with an expected primary load vector.

The interior also includes a cantilevered second flange 1218 which isdefined in part by an undercut groove 1222 formed in the first member1202. The second flange 1218 includes a protruding second contact rim1224. The second contact rim 1224 may have a straight, curved, ortoroidal cross-sectional shape.

The second member 1204 is also made from a rigid material and has awear-resistant, convex contact surface 1228. The first and secondcontact rims 1216 and 1224 bear directly against the contact surface1228 so as to transfer axial and lateral loads from one member to theother while allowing pivoting motion between the two members 1202 and1204. The annular configuration of contact rims 1216 and 1224 results ina joint configuration which permits only pivoting and rotational motion,and is statically and dynamically determinate for the life of the joint1200.

Nominally the first and second contact rims 1216 and 1224 define twoseparate “ring” or “band” contact interfaces with the contact surface1228 of the second member 1204. The flanges 1208 and 1218 (and thus thecontact rims 1216 and 1224) of the first member 1202 are conformable tothe contact surface 1228 when the joint 1200 is placed under load. Theflanges 1208 and 1218 can conform to the imperfect contact surface 1228and deflect in an irregular shape, in the manner described above for thejoint 1200. Any of the flanges described herein may have free shapedefining a first contact area with the contact surface, and a loaded(i.e. deflected) shape defining a second contact area with the contactsurface which is substantially larger than the first contact area,substantially reducing the contact stress between the two members. Thecontact rims 1216 and 1224 and the contact surface 1228 may beconfigured with curvatures to have an asymmetric wear characteristic asdescribed above in detail.

The facing surfaces of either or both of the first and second members1202 and 1204 may include a face layer of a known coating such astitanium nitride, chrome plating, carbon thin films, and/or diamond-likecarbon coatings, and/or a another substantially thicker wear-resistantmaterial such as ultra-high molecular weight (UHMW) polyethylene. Thisface layer is used to impart wear resistance, as described above.

Depending on the specific application, the second flange 1218 may havean angular offset like the first flange 1208. For example, FIG. 40illustrates a prosthetic joint 1200′ substantially similar inconstruction to the prosthetic joint 1200, with first and second members1202′ and 1204′. The first member 1202′ has a balanced centroidal axis“N1′”, and first and second flanges 1208′ and 1218′. The first flange1208′ is angularly offset from the balanced centroidal axis N1′ (i.e. itis asymmetric relative to the balanced centroidal axis N1′) and thesecond flange 1218 is also angularly offset from the balanced centroidalN1′ (i.e. it is asymmetric relative to the balanced centroidal axisN1′).

The flange of the joint members described above need not be circular,elliptical, or another symmetrical shape in plan view, and need not liein a single plane. For example, FIGS. 41-43 illustrate a joint member1302. Its interior defines a cup surface 1306 having a nominal profile.The interior includes a cantilevered first flange 1308, defined in partby an undercut groove 1312 formed in the first member 1302. The firstflange 1308 includes a protruding first contact rim 1316. The firstcontact rim 1316 may have a straight, curved, or toroidalcross-sectional shape. The interior also includes a cantilevered secondflange 1318 which is defined in part by an undercut groove 1322 formedin the first member 1302. The second flange 1318 includes a protrudingsecond contact rim 1324. The second contact rim 1324 may have astraight, curved, or toroidal cross-sectional shape.

The first flange 1308 (and therefore the first contact rim 1316) have a“saddle” shape. In this particular example it has a racetrack shape inplan view, and the portions at the ends of the major axis of theracetrack shape are elevated (in the z-direction) relative to theremainder of the shape. The first contact rim 1316 is shaped so as todefine a contact band in which some or all points on its surface lie ona sphere (or otherwise match the shape of the mating convex joint memberdescribed above). The second flange 1318 could have a similar saddleshape as well.

The prosthetic joints described herein may include one or more flangeswith an open perimeter. For example, FIGS. 44 and 45 illustrate anotheralternative prosthetic joint 1400 comprising first and second members1402 and 1404. The illustrated prosthetic joint 1400 is generallysimilar in construction and function to the prosthetic joint 1000described above, and one or both of the members 1402 and 1404 maybone-implantable as described above.

A balanced centroidal axis “N2”, may be considered to pass through thefirst member 1402. This axis N2 is defined in the same manner as thebalanced centroidal axis “N1” described above. The first member 1402 isconstructed from a rigid material and may generally be thought of as a“cup”, as described above. Its interior defines a cup surface 1406having a nominal profile. The interior includes a cantilevered firstflange 1408, defined in part by an undercut groove 1412 formed in thefirst member 1402. A ramped surface 1414 forms a transition from thegroove 1412 to the nominal cup surface 1406. The first flange 1408includes a protruding first contact rim 1416. The first contact rim 1416may have a straight, curved, or toroidal cross-sectional shape.

The first flange 1408 has an angular offset relative to the balancedcentroidal axis N2, in other words it is asymmetric relative to thebalanced centroidal axis N2. The interior also includes a cantileveredsecond flange 1418 which is defined in part by an undercut groove 1422formed in the first member 1402. The second flange 1418 includes aprotruding second contact rim 1424. The second contact rim 1424 may havea straight, curved, or toroidal cross-sectional shape.

In the example shown in FIGS. 44 and 45, the second flange 1418 is alsoangularly offset from the balanced centroidal axis N2, i.e. it isasymmetric relative to the balanced centroidal axis.

The interior also includes a cantilevered third flange 1429 which isdefined in part by an undercut groove 1430 formed in the first member1402. The third flange 1418 includes a protruding third contact rim1432. The third contact rim 1432 may have a straight, curved, ortoroidal cross-sectional shape. As best seen in FIG. 45, the thirdflange 1429 has an open perimeter, circumscribing less than 360 degrees.The distal ends of the third flange 1429 may be feathered away from thenominal cup surface, for example either by tapering the third flange'sthickness or by tilting the distal ends outward relative to theremainder of the flange, so as not to contact the contact surface 1428of the second member 1404.

The third flange 1429 could be symmetric or asymmetric relative to thebalanced centroidal axis N2.

The second member 1402 is also made from a rigid material and has awear-resistant, convex contact surface 1428. The first, second, andthird contact rims 1416, 1424, and 1432, bear directly against thecontact surface 1428 so as to transfer axial and lateral loads from onemember to the other while allowing pivoting motion between the twomembers 1402 and 1404.

Nominally the first, second, and third contact rims 1416, 1424, and 1432define three separate “ring” or “band” contact interfaces with thecontact surface 1428 of the second member 1404. The flanges 1408, 1418,and 1429 (and thus the contact rims 1216, 1224, and 1432) of the firstmember 1402 are conformable to the contact surface 1428 when the joint1400 is placed under load. The flanges 1408, 1418, and 1429 can conformto the imperfect contact surface 1428 and deflect in an irregular shape,in the manner described above for the joint 1000.

The facing surfaces of either or both of the first and second members1402 and 1404 may include a face layer of a known coating such astitanium nitride, chrome plating, carbon thin films, and/or diamond-likecarbon coatings, and/or a another substantially thicker wear-resistantmaterial such as ultra-high molecular weight (UHMW) polyethylene. Thisface layer is used to impart wear resistance, as described above.

Any of the flanges may have an open perimeter. For example, FIGS. 46 and47 illustrate a prosthetic joint 1400′ similar in construction to theprosthetic joint 1400, including first and second members 1402′ and1404′. The first member 1402′ includes cantilevered first, second, andthird flanges 1408′, 1418′, and 1429′. In this example the first andthird flanges 1408′ and 1429′ have a closed perimeter, and the secondflange 1418′ has an open perimeter, circumscribing less than 360degrees. Any or all of the flanges 1408′, 1418′, and 1429′ may beangularly offset from (i.e. asymmetric relative to) a balancedcentroidal axis “N3” of the first member 1402′, as described above. Theconstruction and function of the joint 1400′ is otherwise identical tothe joint 1400. As described above for the flange 1429, the distal endsof any flange having an open perimeter may be feathered away from thenominal cup surface, for example either by tapering the flange'sthickness or by tilting the distal ends outward relative to theremainder of the flange, so as not to contact the contact surface ofopposing member

FIGS. 48 and 49 illustrate a prosthetic joint member 1502, which may beused with any of the convex joint members described above.

The member 1502 is constructed from a rigid material and generally has aconcave “cup” shape as described above. It may also be bone-implantableas described above. Its interior defines a cup surface 1506 having anominal profile. The interior includes a cantilevered flange 1508,defined in part by an undercut groove 1512 formed in the first member1502. A ramped surface 1514 forms a transition from the groove 1512 tothe nominal cup surface 1506. The flange 1508 includes a protrudingfirst contact rim 1516. The first contact rim 1516 may have a straight,curved, or toroidal cross-sectional shape. The flange 1508 may includean angular offset relative to a balanced centroidal of the joint member1502, as described above.

A peripheral groove 1520 is formed in the cup surface 1506. In theexample shown in FIGS. 48 and 49, it has a “T”-shaped cross-section. Acontact ring 1522 is received in the groove 1520. A part of the contactring 1522 protrudes from the nominal profile of the cup surface 1506 anddefines a second contact rim 1524. In the illustrated example, thecontact ring 1522 has “hat section” cross-sectional shape, with distalflanges that are received in the T-shaped groove 1520.

The contact ring 1522 is made of a rigid material and has awear-resistant surface, as those terms are described above. It is sizedand shaped to achieve controlled elastic deflection, and to beconformable in the manner of the flanges described above. Itsconstruction is thin enough to permit bending under working loads, butnot so thin as to allow material yield or fatigue cracking. Deflectionof the contact ring 1522 is opposed by the elasticity of the contactring 1522 in bending, as well as the hoop stresses therein. To achievelong life, the contact ring 1522 is sized so that stresses therein willbe less than the endurance limit of the material.

Various cross-sectional shapes may be used for the contact ring. Forexample, FIG. 50 illustrates a contact ring 1522′ with a “Z” shape and adoubled-over retention flange 1523. FIG. 51 illustrates a contact ring1522″ with a circular cross-section. The grooves 1520′ and 1520″ aremodified to accommodate their respective contact rings 1522′ and 1522″.

Nominally the first and second contact rims 1516 and 1524 define twoseparate “ring” or “band” contact interfaces with the contact surface ofthe opposed convex member (not shown). The contact rims 1516 and 1524are conformable to an opposed contact surface when the joint is placedunder load.

Any of the joint members described above may include holes or aperturesformed therein to reduce their weight, or to facilitate manufacture orinstallation. For example, FIG. 52 illustrates a cup joint member 1602with first and second flanges 1608 and 1618, and an aperture 1610 formednear the apex of the cup shape.

While the joint members have been illustrated above with monolithicconstruction, any of the joint members may be made from one or morecomponents built up to form the whole. For example, FIG. 53 illustratesa joint member 1702 which is a cup having a first flange 1708 and asecond flange 1718 as described above. The joint member 1702 is made upfrom an annular first section 1710 and a cap-like second section 1711which fit together to form the completed cup shape. The two sections1710 and 1711 are fixed to each other, for example by a mechanical (e.g.interference) fit, an adhesive, welding or other thermal bonding method,or fasteners.

FIG. 54 illustrates a prosthetic joint member 1802, which may be usedwith any of the convex joint members described above.

The member 1802 is constructed from a rigid material and generally has aconcave “cup” shape as described above. It may also be bone-implantableas described above. It is made up from a shell 1804 with an interiorsurface 1806, and a liner 1808 which fits conformally against theinterior surface 1806. The liner 1808 may be fixed or moveable relativeto the shell 1804. An interior of the liner 1808 defines a nominal cupsurface 1810. The liner 1808 includes a first peripheral ring 1812,defined as a generally “U”-shape formed in the liner 1808. The firstperipheral ring 1812 includes a protruding first contact rim 1816. Thefirst contact rim 1816 may have a straight, curved, or toroidalcross-sectional shape. The first peripheral ring 1812 may include anangular offset or asymmetric positioning relative to a balancedcentroidal axis “N4” of the joint member 1802, as that concept isdescribed above.

The liner 1808 also includes a second peripheral ring 1818, defined as agenerally “U”-shape formed in the liner 1808. The second peripheral ring1818 includes a protruding second contact rim 1820. The second contactrim 1820 may have a straight, curved, or toroidal cross-sectional shape.The second peripheral ring 1818 may include an angular offset relativeto a balanced centroidal “N4” of the joint member 1802, as that conceptis described above.

The liner 1808 is made of a rigid material and has a wear-resistantsurface, as those terms are described above. The first and secondperipheral rings 1812 and 1818 are sized and shaped to achievecontrolled elastic deflection, and to be conformable in the manner ofthe flanges described above. Their construction is thin enough to permitbending under working loads, but not so thin as to allow material yieldor fatigue cracking Deflection of the contact rings 1812 and 1818 areopposed by the elasticity of the rings in bending, as well as the hoopstresses therein. To achieve long life, the contact rings 1812 and 1818are sized so that stresses therein will be less than the endurance limitof the material.

Nominally the first and second contact rims 1816 and 1820 define twoseparate “ring” or “band” contact interfaces with the contact surface ofthe opposed convex member (not shown). The contact rims 1816 and 1820are conformable to the opposed contact surface when the joint is placedunder load.

As noted above, known coatings such as titanium nitride, chrome plating,carbon thin films, and/or diamond-like carbon coatings may be used toimpart wear resistance or augment the wear resistance of any of thecontact surfaces and/or contact rims described above. To the same end,it may be desirable to surface treat either or both interfaces of any ofthe above-described implants or joints with a laser, shot peen,burnishing, or water shock process, to impart residual compressivestresses and reduce wear. The benefit could be as much from surfaceannealing and microstructure and microfracture elimination as smoothingitself.

The foregoing has described prosthetic joints with wear-resistantproperties and conformal geometries. While specific embodiments of thepresent invention have been described, it will be apparent to thoseskilled in the art that various modifications thereto can be madewithout departing from the spirit and scope of the invention.Accordingly, the foregoing description of the preferred embodiment ofthe invention and the best mode for practicing the invention areprovided for the purpose of illustration only and not for the purpose oflimitation.

1. A prosthetic joint, comprising: (a) first member having a balancedcentroidal axis, the first member comprising a rigid material andincluding a concave interior defining a cup surface, the cup surfaceincluding: (i) a cantilevered first flange defined by a first undercutin the first member, the first flange defining a wear-resistant firstcontact rim which protrudes relative to a nominal profile of the cupsurface, the first flange being asymmetric relative to the balancedcentroidal axis; and (ii) a cantilevered second flange defined by asecond undercut in the first member, the second flange defining awear-resistant second contact rim which protrudes relative to thenominal profile of the cup surface; (b) a second member comprising arigid material with a wear-resistant, convex contact surface; (c) wherethe first and second contact rims bear directly against the contactsurface of the second member, so as to transfer axial and lateral loadsbetween the first and second members, while allowing pivoting motionbetween the first and second members; and (d) wherein the flanges areshaped and sized so as to deform elastically and permit the first andsecond contact rims to conform in an irregular shape to the contactsurface, when the joint is placed under a predetermined load.
 2. Theprosthetic joint of claim 1, wherein at least one of the contact rimshas a curved or toroidal cross-sectional shape.
 3. The prosthetic jointof claim 1, wherein the surfaces of the first and second members areceramic, metallic, or a combination thereof.
 4. The prosthetic joint ofclaim 1, where the flanges are sized so as to permit elastic deflectionof the flanges while limiting stresses in the flanges to less than theendurance limit of the material, when a predetermined load is applied tothe joint.
 5. The prosthetic joint of claim 1, wherein curvatures of thefirst and second contact rims are different from a curvature of thecontact surface.
 6. The prosthetic joint of claim 1 wherein curvaturesof the first and second contact rims and the contact surface areconfigured to produce an asymptotic wear characteristic when in use. 7.The prosthetic joint of claim 1 wherein one or more of the flanges havea plan view shape which is noncircular.
 8. The prosthetic joint of claim1 wherein at least one of the first and second members comprises atleast two sections fixed together.
 9. The prosthetic joint of claim 1wherein at least one of the flanges has an open perimeter.
 10. Theprosthetic joint of claim 9 wherein distal ends of the open-perimeterflange are feathered away from the nominal profile of the cup surface,so as not to contact the contact surface of the second member.
 11. Theprosthetic joint of claim 1 wherein the cup surface includes a thirdcantilevered flange defined by a third undercut in the first member, thethird flange defining a wear-resistant third contact rim which protrudesrelative to the nominal profile of the cup surface.
 12. The prostheticjoint of claim 11 wherein the third flange has an open perimeter. 13.The prosthetic joint of claim 11 where the third flange is asymmetricrelative to the balanced centroidal axis.
 14. The prosthetic joint ofclaim 1 wherein one or more apertures pass through the first member. 15.The prosthetic joint of claim 1 wherein at least one of the surfacesincorporates a wear-resistant thin film or coating.
 16. The prostheticjoint of claim 1 in which at least one of the members isbone-implantable.
 17. The prosthetic joint of claim 1 wherein at leastone of the flanges has a free shape defining a first contact area withthe contact surface and a loaded shape defining a second contact areawith the contact surface which is substantially larger than the firstcontact area.